Electrical circuits with very high conductivity and high fineness, processes for fabricating them, and devices comprising them

ABSTRACT

This circuit comprises an insulating substrate covered on at least part of its surface by a fine conducting layer (7) whose geometrical form corresponds to the layout chosen for the circuit; the said conducting layer having one or more very fine grooves (9) with a depth of more than 1 μm engraved in the substrate; the groove or grooves (9) being completely filled by at least two superimposed components: the first, situated at the bottom of the groove, consisting of a highly conductive material, (conducting wire or conducting section, or a conducting substance produced by treatment of a liquid, powdery or pastelike precursor material previously positioned in the groove); the second, which seals the groove, being produced by treatment of a liquid powdery or pastelike precursor material (11), which may or may not be conducting; the treatments having imparted to the said precursor materials their solid consistency and their final properties; the conducting layer (7) being deposited in such a way that it is in contact with the conducting components(s) positioned in the groove before filling, at an intermediate stage, or after the sealing of the groove.

FIELD OF THE INVENTION

The present invention relates to electrical circuits with very highconductivity and high fineness, and to the processes used to fabricatethem. The term "conductivity" essentially implies electricalconductivity, but circuits made according to the present invention can,if necessary, be used for their thermal conductivity and contribute tothe transport of calories.

BACKGROUND OF THE INVENTION

The invention also relates to devices comprising these circuits, such aselectrochromic devices, operated in matrices or in segments, for themodulation of light, such as devices for variable reflection or variabletransmission of light, or for the display of signals and images, forexample alphanumeric or graphic data, as well as electroluminescent orliquid crystal display devices; glazing having variable opticalproperties (windows, screens, windscreens), valves, variable-transparency spectacles, variable-reflection mirrors; electric heatingdevices using power current (radiators or convectors, panel heaters);and electronic power circuits, for example amplifier output circuits. Inthese devices, the electrical circuits frequently have to be very fineso that they can be transparent and/or have a high density of conductingelements on a given surface.

At the present time, these electrical circuits are fabricated by a widerange of processes, of which the best known are:

(a) the engraving, for example by acid etching, of conducting layers (ofcopper, for example) deposited on non-conducting substrates such assheets of plastic material which may or may not be fibre-reinforced, orglass plates;

(b) the deposition, by appropriate printing processes, on variousnon-conducting substrates, of conducting tracks consisting of conductinginks or pastes, these tracks corresponding to the circuit design;

(c) the deposition, by various processes of spraying or deposition inthe vapour phase, of a conducting layer on a surface on which a mask haspreviously been deposited; the mask covers the areas of thenon-conducting surface on which the conducting layer is not to bedeposited, and the circuit appears after the removal of the mask by asuitable process, for example by chemical etching; a process of thiscategory, namely photolithography, is used in particular for thefabrication of very fine circuits.

However, these known processes do not enable a number of conditionsnecessary for making certain electrical circuits to be metsimultaneously. For example, photolithography, which can be used to makecircuits with a very low thickness and very high fineness, cannotsimultaneously provide a high linear conduction for the conductors ofthe circuit, owing to their very low thickness. Other processes, such asprinting processes (screen printing, offset, etc.) cannot provide asufficient fineness of the printed lines; moreover, they cannot providea very fine separation of each conducting line from the adjacent line.This difficulty becomes even greater if the conducting area is to becoated with a layer designed to protect it from contact with a corrosiveor conducting medium which might attack or short-circuit it. In order todeposit the conductor and then cover it with one or more protectivelayers, a number of successive passes must be made, positioned correctlywith respect to each other, and it is even more difficult to obtain thedesired fineness.

In certain cases, it is desirable to obtain at the same time anexcellent linear conductivity, a surface whose roughness is close tozero after installation of the circuit, and protection of the circuit.This objective is not attainable with printing processes which, in orderto obtain high conductivity, must deposit a thick layer which then formsan unacceptable relief on the surface of the substrate.

Certain supplementary conditions are sometimes required, and furtherincrease the difficulty of the problem: for example, the production ofcircuits with large dimensions (practically inaccessible tophotolithography), or the provision of a contact between the depositedcircuit and a very thin adjacent conducting layer, to ensure, forexample, uniformity of the electrical potential along the columns (orlines) used in the matrix operation of flat display screens.

The columns (or lines) of these screens are used to introduce datanecessary for the operation and the supply of information relating tothe pixels located along each column. These columns are formed on thesurface of a glass plate by conducting bands resulting from a depositionof metal or oxide which, in order to be transparent, has to be very thin(generally less than one micron) and is consequently a very poorconductor. For example, for a display device only 3 cm wide, an indiumtin oxide (ITO) column with a width of 500 microns produces a resistanceof 300 ohms, which is unacceptable in the case of devices using a veryhigh inrush current (several A per dm²). This low conductivity causes alarge potential difference along the column, which may create seriousproblems if the screen is of large dimensions: the operation of thepixels in the centre becomes very different from that of the pixelslocated at the periphery. It therefore becomes necessary to install,along the transparent column, a fine thick opaque conducting line,located in the black matrix between the pixels, and in contact for thewhole of its length with the column whose conduction it reinforces.However, another difficulty then arises. The fabrication of the screenby certain processes, such as those based on liquid crystals usingcertain effects (twisted nematic and derivatives: STN, smectic A,smectic C*, ferroelectric, etc.) entails a high regularity of theinterface between the electrodes. Thus, in the case of liquid crystaldisplay (LCD) devices, the space must be 5 microns with an accuracy of±0.2 micron, or even of the order of one micron for ferroelectric liquidcrystals. This is incompatible with making reinforcing conductors bydeposits on the surface of the glass which cannot be wide if they are tobe invisible and which must be in relief if they are to be conducting.

Furthermore, for some processes, for example certain electrochromicprocesses, the layer interposed between the electrodes has corrosiveproperties, making it necessary to form the reinforcing conductors insuch a way that they are in electrical communication with thetransparent conducting layer while being protected from the corrosioncaused by the luminophore layer.

The description of this problem illustrates its complexity anddifficulty, to which must also be added the necessity of using aconvenient and fast process to obtain the most favourable productioncosts.

There is a known process, described in U.S. Pat. No. 5,163,220, forraising the electrical conductivity of strips of ITO electrodes in thinfilm electroluminescent (TFEL) display panels. According to thisprocess, grooves are created in the electrode substrate by chemicaletching (using a solution of HF and ammonium fluoride), and thesegrooves are filled by cathode sputtering with successive layers oftitanium, silver and then titanium again (barrier layer). The chemicaletching is carried out after the plate has been heated, enabling thegrooves to be made less open, the inclination α of the side wallschanging from less than 5° to the limit value of 45° (in other words, asshown in FIGS. 1a and 1b, the lateral to vertical etching ratio rchanges from approximately 12:1 to 1:1). With the etching techniquedescribed, the depth of the grooves does not exceed 1 μm in practice.The grooves are filled by cathode sputtering, which only enables verythin layers to be deposited. The ITO strips are deposited subsequentlyto cover the grooves.

Because of the shallowness of the grooves and the thinness of the layerswhich can be made in practice by cathode sputtering, only limitedconductivity can be achieved with the process described in this U.S.patent.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a solution by which itis possible to make, on substrates of insulating material such asmineral or organic glass, circuits with very high conductivity,particularly circuits comprising very fine lines or lines separated byvery fine insulating lines, which may advantageously be protectedchemically from any attack by corrosive elements, and whose transparencyis not significantly affected by the reinforcing conductor.

For this purpose, it is proposed, according to the present invention, toform grooves with a relatively large depth, advantageously delimited bysteep side walls. It then becomes possible to use filling profiles witha relatively large section, permitting high conductivity. Moreover, thisfilling is carried out by techniques which are much easier to apply thancathode sputtering, such as the application of pastes, powders, etc.,making it possible to install very varied combinations of relativelythick conducting and/or protective layers and/or conducting wires, andconsequently to adjust the conductivity according to the environment ofthe circuit, and also permitting different combinations of thesefillings with a thin layer forming the circuit, ensuring the bestcontact with this thin layer.

The initial object of the present invention is therefore an electricalcircuit with very high conductivity and high fineness, designed inparticular to form part of light modulation or display devices ofdifferent kinds such as electroluminescent, electrochromic or liquidcrystal devices, glazing and valves with variable optical properties,electric heating devices using a power current and electronic powersupply circuits, the said circuit comprising:

a substrate made of insulating material;

covered on at least part of its surface by a fine conducting layer whosegeometrical form corresponds to the layout chosen for the electricalcircuit;

the said conducting layer having one or more very fines grooves with adepth of more than 1 μm engraved in the substrate;

the said groove or grooves being completely filled by at least twosuperimposed components:

the first, situated at the bottom of the groove, consisting of a highlyconductive material, namely either a conducting wire or a conductingsection, or a conducting substance produced by treatment of a liquid,powdery or pastelike precursor material previously positioned in thegroove, the said treatment having imparted to the said precursormaterial its solid consistency and its final properties;

the second, which seals the groove, being produced by treatment of aliquid, powdery or pastelike precursor material, which may or may not beconducting, the said treatment having imparted to the said precursormaterial its solid consistency and its final properties;

the conducting layer being deposited in such a way that it is in contactwith the conducting component(s) positioned in the groove, beforefilling, at an intermediate stage, or after the sealing of the groove.

The term "fine conducting layer" shall be taken to mean a layer whosethickness generally varies from 0.05 μm to 0.6 μm.

According to a particularly preferred characteristic, the lateral tovertical engraving ratio r of the groove or grooves is less than 1:1(the side walls are inclined at more than 45°, as illustrated in FIG.1c).

The term "very fine grooves" shall be taken to mean grooves having amean width generally lying between approximately 15 and 80 μm, althoughthese dimensions shall not be considered critical. On the other hand, asa general rule, the depth of the grooves is greater than 6 μm, being inparticular greater than 15 μm and possibly up to 100 μm.

It may be emphasized here that the present invention, which enablesgrooves having a depth of several tens of μm and fillings also havingdepths of several tens of μm to be made, also permits reinforcingconductors for the fine conducting layer positioned on the substratewhich are hundreds of times larger than in the case of the cited U.S.Pat. No. 5,163,220.

The substrate may be in various shapes and the grooves may be disposedin a wide variety of arrangements. Among others, it is possible tomention the case of a flat substrate and rectilinear grooves disposedparallel to each other and interacting with a conducting layer whichcoats the substrate and which is continuous or in the form of stripsparallel to the grooves, with the possibility of associating at leastone groove with one strip. It is also possible to mention circuitsenabling current to be supplied to large pixels cut in a conductinglayer, or for other electronic applications where a high current densityis required in certain parts of the substrate surface.

The conducting wires may comprise a protective conducting coating, andthe said coating may also have undergone, after the installation of thewire, a treatment which consolidates it and gives it its finalproperties.

The precursor materials of the conducting substances are describedsubsequently with reference to the processes according to the invention.It will be noted that the precursor material used to form the groovesealing layer may be a poor conductor or even non-conducting, in whichcase the contact between the fine conducting layer and the groovefilling is made at the level of the conducting layers of the groove.

It is also possible to envisage a case in which the different layersfilling the groove are formed from the same precursor material, in whichcase it might be impossible to distinguish them on completion of thetreatments putting these materials into their final form.

The conducting part of the circuit according to the invention thereforeconsists of at least one conducting substance applied in the groove orgrooves without forming a relief on the surface of the substrate, and acontinuous or discontinuous conducting layer deposited on the support,the conductor or conductors filling the groove or grooves being disposedso that they form supplementary means for supplying current to theconducting layer, means being provided to ensure electricalcommunication between the said layer and these supplementary currentsupply means.

In the latter case, the means providing electrical communication betweenthe conducting layer and the supplementary current supply means may beformed by an extension of the said conducting layer on the internal wallof the groove, or on the upper surface of the said conducting partlocated in the groove, or by conducting strips disposed so that theyconnect the conducting layer to the upper surface of the conducting partlocated in the groove. If the conducting layer is discontinuous, thediscontinuity may be created by a deposition of the layer indiscontinuous parts or by notches or channels made in the substrate,passing through the said layer or lying on one of the upper edges of thegrooves in such a way that it exposes the insulating material formingthe substrate, the said notches or channels possible being filled by anon-conducting material which restores the surface continuity of thesaid substrate.

The present invention also relates to a process of fabrication of anelectrical circuit as specified above, characterized in that:

the groove or grooves are engraved, according to the chosen circuitlayout, in the surface of a substrate made of insulating material,coated if necessary with a thin conducting layer, with possiblesubsequent deposition of a thin layer of conducting material on theparts or on the whole of the surface of the substrate, includinggrooves, if the said substrate has not been previously coated;

the grooves are filled by the introduction of at least one layer ofprecursor material of the conducting layer, which may be a dust or of aliquid to paste-like consistency, appropriate for being applied in thesaid grooves, and/or by the direct positioning of a conducting wirewhich may be provided with a conducting coating, or of a conductingsection, the filling being completed if necessary by a layer of materialin the form of dust or having a liquid to paste-like consistency, whichis the precursor of a conducting or non-conducting protective layerwhich is neutral with respect to its environment;

after the positioning of at least one precursor material, this materialis appropriately treated to give it its final shape, consistency andproperties, a thin layer of conducting material, in the case of apreviously uncoated substrate, possibly being deposited during thefilling of the grooves, on parts or all of the substrate, includinggrooves, between two layers of filling of the grooves, or depositedafter the filling of the grooves on parts or all of the substrate; and

in the case in which the external thin layer has to be discontinuous,notches or channels are formed in such a way as to expose the substrateof insulating material, according to the chose circuit layout, thenotches or channels possibly being filled subsequently by anon-conducting material.

In order to engrave steep-sided grooves according to the invention inthe surface of the substrate, a thermal, mechanical-thermal, mechanical,mechanical-chemical or electric process may be used.

(1) The use of a laser, for example a UV excimer laser, may be cited asa thermal process. This method has the advantage of permitting theengraving of extended and complex circuits with a minimum ofmanipulation of the substrates and with a high production rate. In thisway it is possible to obtain very fine grooves positioned with highprecision and with a very clean profile.

(2) Pressing, injection and upsetting may be cited as mechanical-thermalprocesses. In the case of pressing, a drop of glass (a parison),delivered from a feed device, falls freely on to the base of a mould,after which a punch having ridges designed to form the grooves pressesthe drop of glass while engraving the imprint of the punch in the softglass. In the case of injection, a drop of glass is received in a pistonwhich injects the glass into a closed mould by the effect of pressure.In the case of upsetting, a sheet of glass having the final dimensionsis preheated gently to above the softening point, and is then subjectedto a pressure which stamps the engraving.

(3) The mechanical processes are sandblasting, lapping and grinding. Inthe last case, a grinding wheel or circular saw is used. Progress madein recent years in this field and in the corresponding machines is suchthat it is entirely possible to obtain the necessary precision andfineness and to avoid breaking the substrates.

(4) High-pressure water jets and ultrasonic machining may be cited amongthe mechanical-chemical processes.

(5) Erosion caused by the contact of the glass with a platinum wirebrought to red heat by the Joule effect may be mentioned as anelectrical process. This process is known under the name of Plantee anda variant of it is known under the name of Phelps (see Nouveau ManuelComplet du Verrier, Julia de Fontenelle and F. Malepeyre, Volume II,pages 41-43).

The successive layers of precursor material can advantageously beinstalled by application of a substance in dust form or having a liquidto paste-like consistency of the precursor material on the surface ofthe substrate bearing the grooves and the removal of the substance whichhas not penetrated into the grooves, or by application of a paste or inkwith a squeegee or with the aid of an inking roller, possible after theexecution of a treatment, before the formation of the grooves, designedto make the surface of the substrate non-wettable by the ink, so thatthe applied ink flows virtually exclusively into the grooves.

One example which may be mentioned is the use of a metal powder, such asa zinc, tin, or silver powder, which is made into a paste with water bymixing with the precise quantity of water necessary to fill the voidsbetween the grains (grains with a diameter significantly smaller thanthe width and depth of the grooves are used). These pastes haveapproximately the viscosity of toothpaste and may be positioned in thegrooves with a simple rag or an inking roller.

The use of an ink, such as an ink suitable for screen printing, may alsobe mentioned, for example the "hybrid thick film" technology. Such inksmay be, for example, vinyl, phenol or epoxy inks, based on silver,copper or gold, etc., whose viscosity has been adjusted to enable themto be applied by screen printing. They may conveniently be positioned inthe grooves by using a squeegee as in screen printing.

It is also possible to apply in the grooves metal wires, for examplecopper wires, whose diameter is smaller than the depth of the groove.This operation which is relatively delicate is performed better if thewire is coated with a fine protective layer, for example a layer ofthermoplastic or thermosetting polymer. Since the wire has to be inelectrical contact with the exterior, the polymer is filled with powder,such as graphite or conducting carbon, so that it becomes a conductoritself. A complementary layer, for example one consisting of the samepolymer which may be a conductor, is added to finish the filling of thegroove. If necessary, gentle polishing enables a uniform surface to berestored.

Finally, the precursor material applied in a groove is given its finalshape and/or structure by fusion to reconstitute the analogue of a metalwire by heat treatment by microwaves or infrared radiation, in the caseof a metal powder or a metal powder made into a paste with water or aconducting ink; by drying in the case of a paste or ink of the type usedin screen printing or of the type filled with carbon to form aconducting adhesive, by the evaporation of the water or solventcontained in it; or by polymerization or setting in the case ofpolymerizable compounds or thermosetting polymer compounds.

If a metal powder is used, in its original form or in the form of apaste made with water, the fusion reconstitutes a true metal wire havingthe corresponding conductivity. This fusion is advantageously performedin a reducing atmosphere, for example N₂ +5% by volume of H₂. In thesame way, a conducting ink based on a metal powder (copper, for example)can be treated in a microwave oven to form the conductor after thegrooves have been filled.

If a metallic paste or ink of the type developed for use in screenprinting has been used, drying may be carried out to obtain a solidlayer where conductivity will be lower than that of solid metal, but maysuffice in many cases.

It is also possible to use, by the same technique, polymer inks filledwith carbon or conducting adhesives or polymer compounds filled withmetal powders, which have the advantage of being passive in relation toany physical and chemical attack, even if their conductivity is somewhatlower. Moreover, they may be used in particular to protect theconductors created by the other methods indicated.

It is also possible to make one of the filling layers by chemicaldeposition or electrolytic deposition. For example, the bases of thegrooves may be made conducting by chemical precipitation, tin-plating,silver-plating, gold-plating, platinum-plating, copper-plating, etc.,and this deposit may be used if necessary as the starting electrode togrow a thicker layer, of copper for example, by electrotyping. Ifnecessary, it is also possible to deposit fine layers, of SnO₂ or ITOfor example, by cathode sputtering or by a CVD process. However, this isnot to be preferred, since these techniques can only be used to producea few hundred nanometers of metal plating, whereas the grooves accordingto the invention have a depth of more than 1 micron.

Finally, the present invention is also applicable to the devicescomprising the circuits as described above.

Devices which may be mentioned include a light modulation device, suchas an electrochromic device for light modulation, a display device withliquid crystals and the other types cited above, glazing or a valve withvariable optical properties comprising two substrates of which onecarries a circuit of electrodes and the other a circuit of counterelectrodes, the two circuits being disposed facing each other with theinterposition of a luminophore layer, in which case at least one of thetwo electrode circuits is as specified above. As devices of this type,illustrated below, it is possible to cite screens or display unitsconsisting of cells operated in a matrix mode, the circuits ofelectrodes and counter electrodes consisting respectively of parallelconducting columns and parallel conducting lines, disposedperpendicularly to the columns, at least the electrode circuitconforming to the invention. It is also possible to cite glazing orvalves with variable properties, also illustrated below, both of whosecircuits conform to the invention, with the possibility of providingmeans to ensure the independent control of the potential of theconducting parts of each groove and, if necessary, of the externalconducting layer associated with the groove if this layer isdiscontinuous.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate further the object of the present invention, someembodiments of the invention are described below, for information andwithout restriction, with reference to the attached drawing.

In this drawing,

FIG. 1, to which reference was made above, represents schematicallysections of a groove according to the prior art and according to theinvention;

FIG. 2 is a partial schematic view, in transverse section, on anenlarged scale, of an electrochromic matrix screen whose electrodecircuit forming the columns of the screen is made according to thepresent invention;

each of FIGS. 3 to 6 illustrates a process of fabricating a variantembodiment of this electrode circuit, showing, in each case, thesuccessive stages of formation of the columns on part of the base plate,represented on an even larger scale;

each of FIGS. 7 to 9 illustrates, in transverse section, anotherpossible variant embodiment of the conducting part filling a groove ofthis electrode circuit;

FIG. 10 is a schematic view of a direct addressing display panel elementcomprising an electrical circuit according to the present invention; and

each of FIGS. 11 and 12 represents a partial schematic view intransverse section at the enlarged scale of glazing having variable andcontrollable optical properties comprising electrode circuits accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

If reference is made initially to FIG. 2, it will be seen that anelectrochromic matrix screen 1, having a known structure, isrepresented, and comprises a first transparent supporting plate 2carrying the operating electrodes 3 which are transparent, and a secondsupporting plate 4, separated transversely from the plate 2 and carryingcounter electrodes 5, the plate 4 and the counter electrodes 5 possiblybeing made of transparent material, at least one layer 6 of electrolyticmaterial whose composition exhibits electrochromism (luminophore orchromogenic material) being disposed between the electrodes 3 and thecounter electrodes 5.

The transparent plate is made from mineral glass or organic glass. Sometypes of organic glass which may be mentioned are, in particular,polymethylmethacrylate, polycarbonates, aminoplastics, urea resins andallyl resins; polyesters and polyurethanes may also be mentioned.

The electrodes 3 are in the form of conducting strips 7, also called"columns" of the screen, are transparent and parallel and have athickness varying from a few hundred to a few thousand angstroms, with awidth varying from 200 to 500 μm, separated by intervals of 20 to 100μm, which represent what is known as the "black matrix"; the transparentconducting layer forming the strips 7 consists of one or more metals oroxides, such as gold, silver, tin oxide (TO), mixed indium and tin oxide(ITO), zinc oxide and cadmium stannate, etc., as mentioned in theliterature; each of these columns 7 is also, along one of its edgeareas, and in the various ways which will be described below, in contactwith a supplementary current supply column 8, between the two ends ofthe associated column 7, in other words inside the screen itself. Theassembly of the columns 7 and the supplementary columns 8 constitutesthe conducting part of an electrical circuit according to the presentinvention.

The counter electrodes 5 are in the form of conducting strips parallelto each other, and are also called the "lines" of the screen, since theyare disposed perpendicularly to the columns 7.

These counter electrodes 5, which are not necessarily transparent, willnot be described further here. If they are transparent, it is possiblefor them to have the same structure as the electrodes 3 (columns 7 andsupplementary columns 8).

The screen 1 is completed, in a known way, by means of supplying theelectrical current to the ends of the columns 7+8 and the lines 5, andby means of applying electrical signals to these columns 7+8 and lines5, in order to generate, under the application of an electrical signaladdressed simultaneously to a line and a column a luminous effect in theluminophore material 6 at the intersection of the line and column.

The supplementary columns 8 are formed in the grooves 9 made in thesurface of the plate 2, advantageously in such a way that they lie onthe "black matrix" as far as possible.

Some of the possible variant embodiments of these columns 7 and 8 willnow be described.

(1) A first variant is represented in FIG. 3. This uses an uncoatedglass plate 2 in which parallel grooves 9, having a depth of the orderof 30-100 μm and a mean width of the order of 30-80 μm, are engraved atintervals chosen according to the specified dimensions of columns 7+8,by one of the processes described above, these grooves 9 comprising, forexample, a relatively flat bottom and sides flared slightly in thedirection of the surface of the plate 2 (FIG. 3a).

A conducting base layer 10, for example a silver or copper paste, ispositioned in these grooves 9, by one or other of the techniquesdescribed above, followed by an upper protective and conducting layer11, for example graphite or conducting carbon, the latter layercompleting the filling of the grooves 9 (FIG. 3b).

A fine layer 12, with a thickness of the order of 0.2-0.9 μm, of theconducting metal or oxide designed to form the columns 7 is thendeposited on the totality of the surface of the plate 2, by cathodesputtering or the CVD process (FIG. 3c).

Finally, to form the columns 7+8, shallow notches 13 parallel to thegrooves 9 are formed by a process such as that described above in theplate 2, at the same interval as that separating the grooves, each notchbeing situated in the vicinity of a groove 9 and being cut through thelayer 12 and into the underlying glass to expose the insulating materialof the substrate 2 (FIG. 3d₁).

To ensure the alternation of the conducting parts and the insulatingparts on the plate 2, it is also possible, as shown in FIG. 3d_(d), toform longitudinal channels 14 so that each of these lies on one of theedges of a groove 9, exposing the insulating material of the substrate 2in part of the said channels 14. If perfect smoothness of the plate 2 isrequired, the channels 14 may be filled with a material 15 which isnon-conducting, is advantageously transparent, and can be set, forexample a thermosetting polymer.

The contact between the columns 7 and 8 is made, in the case of thisvariant, over the totality or almost the totality of the surface of thelayer 11.

The function of the layer 11 in protecting the layer 10 from corrosionby the luminophore material 6, which is assumed to be corrosive, as isfrequently the case in practice, may also be emphasized.

(2) A second variant is described with reference to FIG. 4. In thiscase, after the grooves 9 have been formed as in the case of the firstvariant (FIG. 4a), a layer 12 of the transparent conducting materialwhich is to form the columns 7 is deposited by cathode sputtering or theCVD process, in such a way that it covers the whole of the plate 2 (FIG.4b). The layers 10 and 11 are then applied successively as in the caseof the first variant (FIG. 4c), the surfaces of the layers 11 being intoalignment with the surface of the layer 12 in this case. To complete theformation of the columns 7+8, there are two possibilities, asillustrated in FIGS. 4d₁ and 4d₂, which are analogous to the embodimentsshown in FIGS. 3d_(a) and 3d₂ respectively. The formation of the grooves13 and of the channels 14 with their filling material 15 will not,therefore, be described in further detail at this point.

In the case of the second variant, a column 8 (layers 10 and 11) and theassociated column 7 (formed by the external adjacent strip of the layer12) are in contact along the whole of the part of the layer 12 locatedinside the groove 9. In this case, therefore, the columns 7 aretherefore very well supplied with current by the supplementary columns8.

(3) A third variant is now described with reference to FIG. 5. Thisvariant will not be described in detail, since it differs from thepreceding variant only in that the layer 12 is applied over the totalityof the plate 2 (FIG. 5c) after the formation of the grooves 9 (FIG. 5a)and the application of the base layers 10 (FIG. 5b). After thedeposition of the layer 12, the filling of the grooves 9 with the layer11 is completed (FIG. 5d), after which, in the same way as in the twopreceding variants, either the grooves 13 are formed (FIG. 5e₁) or thechannels 14 (FIG. 5e₂) are formed and filled by the material 15.

The electrical communication between the column 8 and the associatedcolumn 7 is very well reinforced in this case. Since part of the layer12 is simultaneously in contact with the layer 10 and with the layer 11within the groove 9.

(4) A fourth variant will now be described with reference to FIG. 6. Acommercially available plate 2, pre-coated with a layer 12, is used(FIG. 6a).

According to a first embodiment, illustrated in FIGS. 6b₁ to 6e.sub. 1!,grooves 9 (FIG. 6b₁) are formed in the pre-coated plate 2, and thelayers 10 and 11 are then applied in these grooves, the layers 11 cominginto alignment with the parts 12 (FIG. 6c₁). Strips 16, having a widthof 80-100 μm and a thickness of the order of 4-8 μm, of a conducting andprotective material, identical to or of the same type as the materialconstituting the layers 11 (FIG. 6d₁), are then deposited by screenprinting so that they link the layer 12 and the surface of the layers11. The electrical contact between the columns 7 and 8 is made in thiscase through the intermediary of these strips 16.

Finally, either notches 13 or channels 14 are formed as in the case ofthe preceding variants (FIGS. 6e₁ and 6e₂ respectively).

According to a second embodiment, illustrated in FIGS. 6b₂ and 6d₂, thegrooves 9 and the notches 13 are formed simultaneously at the outset(FIG. 6b₂). The layers 10 and the layers 11 are then appliedsuccessively in the grooves 9 (FIG. 6c₂), care being taken not to fillthe notches 13. For this purpose, it is possible, for example, todeposit at the bottom of each of these notches 13 a wire of a plastictype whose diameter matches the width of the notch. After the operationsof filling the grooves 9, the wires are extracted, thus freeing the saidnotches.

FIGS. 7 to 9 show other embodiments of the filling of the grooves 9,which may be used in one of the variants which were described above.Those skilled in the art will understand that there are also otherpossibilities for filling the grooves 9, for example by combining theseembodiments with each other.

In the groove 9 according to FIG. 7, a conducting wire 17 having adiameter of the order of 30-70 μm is installed, and is coated with aconducting and protective layer 18, for example a polymer filled with aconducting powder, the diameter of the coated wire being approximatelyequal to the width of the groove 9 at mid-depth, or alternatively beingsmaller. The filling is completed by the application of a conducting andprotective paste 11 of the same type as the layer 11 in the variantsshown in FIGS. 3 to 6. This variant of the filling of the groove 9 mayreplace, for example, those shown in FIGS. 3 to 6.

In the case of the variant shown in FIG. 8, a conducting layer 10 of thesame type as the layer 10 in the variants shown in FIGS. 3 to 6 has beenapplied in the bottom of the groove 9, after which an uncoatedconducting wire 17 has been positioned and the filling has beencompleted with a conducting and protective layer 11. This variant of thefilling of the groove 9 may replace, for example, those shown in FIGS.3, 6 and 7.

The groove 9 shown in FIG. 9, covered with a layer 12, as in FIGS. 4 and6, has a filling identical to that shown in FIG. 8. It would also bepossible to envisage, for example, a filling of the type shown in FIG.7.

FIG. 10 shows schematically the seven chromophore segments 19 (or largepixels) of a known display panel of the direct addressing type, designedto display an alphanumeric character. Each of these segments 19 consistsof a layer of electrolytic material situated between a working electrodelayer, consisting of tin oxide for example, and a counter electrodelayer. A current supply and reinforcement circuit 20, made according tothe invention with grooves made in the associated substrate and filledwith conducting material, such as a copper- or silver-based adhesive orink which may be protected, has also been shown schematically for one ofthese pixels. A circuit of the same type is associated with each pixel.This figure shows a disposition of grooves different from that withparallel rectilinear grooves.

If reference is made now to FIG. 11, it will be seen that this showsglazing with variable properties, consisting, in a known way, of twoglass substrates 22, spaced apart, each of which carries a circuit ofelectrodes 23, the electrodes 23 being disposed facing each other withthe interposition of a luminophors layer 26, for example one comprisingin a known way a transition metal salt, such as WO₃ (electrochromiclayer) or liquid crystals dispersed in a polymer (PDLC).

The structure of the electrodes 23 is practically analogous to that ofthe "columns" of the screen shown in FIG. 2; in other words, theelectrodes consist of parallel conducting strips 27, made for example ofTO or ITO, each having its conductivity reinforced by a conducting part28 filling a groove 29, and with the whole of its upper surface incommunication with the associated strip 27.

The grooves 29, practically of the same size as the grooves 9 describedpreviously, are parallel to each other and spaced equally at intervalsof 50 to 1000 μm, and are made in the two plates 22, the grooves 29 ofone plate being staggered by one half-interval with respect to thegrooves 9 of the other plate. However, any other relative disposition ofthe grooves 29 may also be envisaged.

Different modes of filling the grooves 29 are possible, such as thoseshown in FIGS. 3 to 6, 3d₁ or 3d₂, or 4d₁ or 4d₂, or 5e₁ or 5e₂, or 6e₁,6e₂, or 6c₂ or 6d₂, 7, 8 and 9.

The strips 27 have a width of the order of 200-1000 μm and they arespaced apart by an equal distance of the order of 50-200 μm.Additionally, although the strips 27 formed on one plate 22 arerepresented in FIG. 11 as being disposed in a staggered arrangement withrespect to those of the other plate 22, other dispositions are possible.In the glazing shown in FIG. 11, it is possible to control the potentialof the strips 27+28 independently.

FIG. 12 shows another variant embodiment of glazing with variableproperties, which differs from the preceding embodiment in that thestrips 27 are replaced by continuous layers, permitting only oneequipotential voltage control on each layer 27. In this case, theconducting parts 28 allow the uniformity of the colour to be improvedover the whole of the glazing 21. FIGS. 3c, 4c, 5d, 6c₁ and 6d₁ showother possible structures for the combination of the plates 22 and theelectrodes shown in FIG. 12, also in combination with the variants shownin FIGS. 7 to 9.

The following examples provide further illustrations of the presentinvention.

EXAMPLE 1 (See FIG. 3b)

In a 2 mm thick glass plate 2, previously surface treated by spraying acommercially available hydrophilic product, grooves 9, with a mean widthof 35 μm and a depth of 30 μm, were formed with the aid of a "DISCO DAD2 H6/T" saw using diamond-impregnated blades. This saw, which iscommonly used for cutting silicon chips, has a precision of the order ofa micron in each of the three dimensions. In this way a very regularnetwork of 150 parallel grooves 9, spaced 350 μm apart, was created.

Several layers of a silver paste (ACHESON, DEMETRON, MINICO) weredeposited in these grooves 9 with a screen printing squeegee, giving atotal thickness of 25 μm. After firing at approximately 120°-150° C.,conducting parts 10 having a resistance of approximately 4 ohms per 3 cmof width of the plate were obtained in the grooves 9. The filling of thegrooves 9 was then completed by the deposition of a layer 11 ofprotective graphite-impregnated ink (MINICO series 5000) (25 Ω/cm per 10μm of thickness), which was heat polymerized.

Corrosion tests have shown that the conducting network formed in thisway was completely protected from corrosion by an environment with pH 2.

EXAMPLE 2 (See FIG. 8)

Grooves 9 having a width and depth of approximately 50 μm were createdby the same process as in Example 1 in a 2 mm thick glass plate 2, atintervals of 500 μm.

A layer 10 of carbon-impregnated ink with a thickness of 10 μm wasdeposited on the plate by the technique described in Example 1. Beforethe ink 10 was dried, copper wires 17 with a diameter of 30 μm wereapplied in the grooves 9 with the aid of a "Wedge Bonding" instrument ofthe KULICKE and SOFA or PRECIMECA type, making it possible to carry outa first soldering on a metal substrate external to the glass plate 2, toextend the wires 17 in the grooves 9, and then to carry out a secondsoldering while extending and cutting the wires 17. In this way ahundred wires 17 were disposed in the grooves 9. The filling of thegrooves was then completed with layers 11 of protectivegraphite-impregnated ink of the same type as that used in layer 11 inExample 1.

In this way resistances of the order of 0.06 Ω/cm of length of thegroove were obtained.

EXAMPLE 3 (See FIG. 11)

In a 2 mm thick glass plate 22, previously surface treated by acommercially available hydrophobic product, parallel grooves 29 with awidth of 30 μm and a depth of 30 μm were engraved at intervals of 300 μmwith the aid of a LUMONIX EXCIMER UV laser, using a wavelength of 193nanometers and pulses of 10 to 30 ns at a frequency of 200 Hz. Adigitally controlled positioning table enabled this process to becarried out with an accuracy of 1 μm.

The grooves 29 obtained in this way were then filled to half their depthwith a metal paste obtained by mixing tin powder and lead powder in aratio of 60/40 by weight with a precisely sufficient quantity of water.The conducting parts were formed by fusion of the powders by heating theplate 22 in a furnace with a reducing gas circulation (for example, 4%hydrogen in nitrogen) at a temperature above the melting point of themetal powders constituting the paste.

The filling of the grooves is completed with a conductingcarbon-impregnated ink by the method described in Example 1. A layer ofITO covering the glass 22 and the filled grooves 29 is then deposited bycathode sputtering. This is then engraved by known methods into strips27, parallel to the grooves, 250 μm wide and spaced 50 μm apart, thestrip 27 lying on top of the groove.

Two identical glass plates are disposed facing each other, so that thegrooves 29 of one plate are staggered by a half-interval with respect tothe grooves 29 of the other plate. These two glass plates encapsulate anadhesive coated transparent linking polymer in which liquid crystals aredispersed. This cell, assembled in the above way, forms glazing withvariable properties which are controllable over all or part of thesurface according to the electrical connections made.

EXAMPLE 4 (See FIG. 4)

In a 2 mm thick glass plate 2, parallel grooves 9 separated by intervalsof 350 μm were created by the process described in Examples 1 and 2,with the aid of an 80 μm diamond-impregnated blade to a depth of 30 μm(FIG. 4a).

The plate 2 was then subjected to a cathode sputtering treatment, whichcovered it entirely, including the internal walls of the grooves 9, witha fine layer 12 of transparent tin oxide 0.4 μm thick (FIG. 4b).

A silver layer 10, followed by a layer of protectivegraphite-impregnated ink 11 which had been polymerized, was then appliedin the grooves 9 by the process described in Example 1 (FIG. 4c).

A DISCO machine was used to form channels 14, 20 μm wide and 2 to 6 μmdeep, each channel lying on one of the edges of the grooves 9 which hadbeen filled as described, thus exposing the glass in approximately onehalf of each channel 14. In order to restore the perfect smoothness ofthe plate 2, the channels 14 were then filed with a polymerizablecompound 15 of insulating ink which was set at 150° C. (FIG. 4d₂).

This produced a substrate 2 comprising conducting columns 7, separatedby insulating polymer surfaces 15 and very well supplied with current bythe supplementary columns 8 formed by the conducting parts 10 and 11positioned in the corresponding grooves 9. The columns 8 are in verygood electrical communication with the columns 7 owing to the contactwith the layer 12 of tin oxide located in the grooves 9.

It is to be understood that the embodiments described above are not inany way restrictive and may be subjected to any desirable modificationswithout departure from the scope of the invention.

We claim:
 1. An electrical circuit, comprising:an insulating substratehaving one or more grooves of a depth of more than 6 μm engraved into asurface of said substrate, each said groove being completely filled byat least two superimposed components, including:a conductive materialplaced in a lower portion of said groove; and a protective materialplaced over said conductive material for sealing said groove; and aconducting layer covering at least part of a surface of said substrate,said conducting layer having a geometrical form corresponding to anelectrical circuit layout, said conducting layer being electricallyconnected with said conductive material, wherein said conductivematerial is disposed in the form of a precursory material and whereinsaid precursory material introduced into each groove is brought into itsfinal form by drying for the purpose of evaporating water or solventscontained therein.
 2. An electrical circuit, comprising:an insulatingsubstrate having one or more grooves of a depth of more than 6 μmengraved into a surface of said substrate, each said groove beingcompletely filled by at least two superimposed components, including:aconductive material placed in a lower portion of said groove; and aprotective material placed over said conductive material for sealingsaid groove; and a conducting layer covering at least part of a surfaceof said substrate, said conducting layer having a geometrical formcorresponding to an electrical circuit layout, said conducting layerbeing electrically connected with said conductive material, wherein saidconductive material is disposed in the form of a precursory material andwherein said precursory material introduced into each groove is broughtinto its final form by polymerization.
 3. An electric circuit,comprising:an insulating substrate having one or more grooves of a depthof more than 6 μm engraved into a surface of said substrate, each saidgroove being completely filled by at least two superimposed components,including:a conductive material placed in a lower portion of saidgroove; and a protective material placed over said conductive materialfor sealing said groove; and a conducting layer covering at least partof a surface of said substrate, said conducting layer having ageometrical form corresponding to an electrical circuit layout, whereinsaid conductive material is applied into said groove without forming arelief on the surface of said substrate, said electrical circuit furthercomprising: means for electrically coupling said conducting layer andsaid conductive material, wherein said protective material isconductive, wherein said electrically coupling means includes saidprotective material for electrically coupling said conductive materialwith said conducting layers, and wherein said electrically couplingmeans includes a conductive strip disposed onto the surface of saidsubstrate for electrically coupling said conductive material with saidconducting layer.
 4. An electrical circuit, comprising:an insulatingsubstrate having one or more grooves of a depth of more than 6 μmengraved into a surface of said substrate, each said groove beingcompletely filled by at least two superimposed components, including:aconductive material placed in a bottom portion of said groove; and aprotective material placed over said conductive material for sealingsaid groove; and a conducting layer covering at least part of a surfaceof said substrate, said conducting layer having a geometrical formcorresponding to an electrical circuit layout, said conducting layerbeing electrically connected with said conductive material,wherein saidconductive material is applied into said groove without forming a reliefon the surface of said substrate, and wherein said conducting layerfurther includes a notch made through said conducting layer and in saidsubstrate to create a discontinuity in said conducting layer by exposingsaid substrate.
 5. An electrical circuit, comprising:an insulatingsubstrate having one or more grooves of a depth of more than 6 μmengraved into a surface of said substrate, each said groove beingcompletely filled by at least two superimposed components, including:aconductive material placed in a bottom portion of said groove; and aprotective material placed over said conductive material for sealingsaid groove; and a conducting layer covering at least part of a surfaceof said substrate, said conducting layer having a geometrical formcorresponding to an electrical circuit layout, said conducting layerbeing electrically connected with said conductive material, wherein saidsubstrate is flat, and wherein said grooves are rectilinear and parallelto each other and interacting with said conducting layer, wherein saidconducting layer is deposited on the substrate to coat said substrate,wherein said conductive material is applied into said groove withoutforming a relief on the surface of said substrate, wherein saidprotective material is conductive; and a conductive strip disposed ontothe surface of said substrate for electrically coupling said conductivematerial with said conducting layer, at least one groove beingassociated with one strip.
 6. A process of fabricating an electricalcircuit on the surface of an insulating substrate, the processcomprising the steps of:(a) engraving a groove in the surface of saidsubstrate; (b) disposing a conductive material into said groove; (c)treating said conductive material to place it in a final state; (d)filling said groove with a protective material after step (c); (e)treating said protecting material to place it in a final state afterstep (d); and (f) coating said substrate with a conductive layer,wherein said coating step is performed prior to step (a).
 7. A processof fabricating an electrical circuit on the surface of an insulatingsubstrate, the process comprising the steps of:(a) engraving a groove inthe surface of said substrate; (b) disposing a conductive material intosaid groove; (c) treating said conductive material to place it in afinal state; (d) filling said groove with a protective material afterstep (c); (e) treating said protecting material to place it in a finalstate after step (d); and (f) coating said substrate with a conductivelayer, wherein said coating step is performed after step (a), but beforestep (b).
 8. A process of fabricating an electrical circuit on thesurface of an insulating substrate, the process comprising the stepsof:(a) engraving a groove in the surface of said substrate; (b)disposing a conductive material into said groove; (c) treating saidconductive material to place it in a final state; (d) filling saidgroove with a protective material after step (c); (e) treating saidprotecting material to place it in a final state after step (d); and (f)coating said substrate with a conductive layer, wherein said coatingstep is performed after step (c), but before step (d).
 9. A process offabricating an electrical circuit on the surface of an insulatingsubstrate, the process comprising the steps of:(a) engraving a groove inthe surface of said substrate; (b) disposing a conductive material intosaid groove; (c) treating said conductive material to place it in afinal state; (d) filling said groove with a protective material afterstep (c); (e) treating said protecting material to place it in a finalstate after step (d); and (f) coating said substrate with a conductivelayer, wherein said coating step is performed after step (e).
 10. Aprocess of fabricating an electrical circuit on the surface of aninsulating substrate, the process comprising the steps of:(a) engravinga groove in the surface of said substrate; (b) disposing a conductivematerial into said groove; (c) treating said conductive material toplace it in a final state; (d) filling said groove with a protectivematerial after step (c); (e) treating said protecting material to placeit in a final state after step (d); and (f) coating said substrate witha conductive layer, wherein said conductive material is a conductivewire, and wherein step (b) further includes covering said conductivewire with a conductive precursory material appropriate for applying intosaid groove.
 11. A process of fabricating an electrical circuit on thesurface of an insulating substrate, the process comprising the stepsof:(a) engraving a groove in the surface of said substrate; (b)disposing a conductive material into said groove; (c) treating saidconductive material to place it in a final state; (d) filling saidgroove with a protective material after step (c); (e) treating saidprotecting material to place it in a final state after step (d); and (f)coating said substrate with a conductive layer, wherein said conductivematerial is introduced as precursory material and then treated to impartits final properties, wherein precursory material not residing in saidgroove is defined as excess precursory material, the process furthercomprising the step of removing excess precursory material before theirrespective treating steps.
 12. The process of claim 11, furtherincluding:treating the surface of said substrate to make the surfacenon-wettable thereby causing said precursory material to flow virtuallyexclusively into said groove.
 13. The electrical circuit of claim 4,wherein said notch includes a channel formed through said conductinglayer and into an upper edge of said groove.